Research Highlights

Aquaculture/Fisheries Center Research Highlights

Nutrition

Effect of different lipid supplements in practical diets on performance of channel catfish
Rebecca Lochmann

To retain the advantages of current catfish production practices while improving the economics of production and/or increasing the attractiveness of catfish from a human health standpoint, we are testing whether existing commercial catfish formulations can be supplemented with small amounts of plant-derived n-3 and n-6 essential fatty acids, or conjugated linoleic acid (CLA’s) from vegetable oil to improve fish performance and/or the nutrient profile of the fish for humans.

A commercial 32%-protein catfish feed was ground and repelleted with different lipid supplements: 1)arachidonic acid (ARA), 2)docosahexaenoic acid (DHA), 3) a mixture of ARA and DHA (50/50%), or 4) conjugated linoleic acid (CLA). One additional diet was not supplemented (control). A feeding trial (10 weeks) was conducted in 110-L aquaria in a flow-through system. Each diet was fed to four tanks of eight fish averaging 5.7 g initially at a rate of 4-5% divided into two feedings. Fish were weighed every two weeks. At the end of the trial final weights were obtained. Lysosome and alternative complement activity were each measured in four fish per tank (16 individual fish per assay per treatment). Bled fish carcasses were frozen prior to analysis of proximate composition.

Fatty acid supplements significantly increased the levels of healthy fatty acids in fish muscle, indicating the practical potential for manipulating channel catfish composition to benefit human health. These value-added products may cost more but will cater to the increasingly health-conscious public who now see coldwater fish as their only option to increase their n-3 fatty acid intake.
Nutrition, immunity, economics, and field demonstrations of sunshine bass
Rebecca Lochmann and Steve Rawles

Hybrid striped bass producers would like to include more carbohydrates in the diets of these carnivorous fishes for cost reasons. Certain types of carbohydrates are used better than others in mammals, and manipulating the ratios of these carbohydrates in fish diets may improve their utilization also. Hybrid striped bass producers and human consumers of these fish are potential beneficiaries.

A series of feeding trials has been conducted in tanks under controlled conditions at SNARC. The fish have received diets with different amylose:amylopectin ratios to try and improve carbohydrate utilization. Growth, survival and body composition data as well as data addressing the cellular impact of these diets was collected.

Fish fed glucose had the greatest number of responses that were different from fish fed diets with different ratios of amylose and amylopectin. Proximate analysis of tissues showed the same pattern. Many of the blood lipids did vary by diet, but again the main contrast was in fish fed the glucose diet versus all others. Our results indicated that manipulating the ratio of amylose to amylopectin in diets did not affect the utilization of carbohydrates in this species, in contrast to mammals. However, there are many potential variations that have not been tested in these fish and the economic incentive to continue testing carbohydrate combinations in diets for hybrid striped bass is strong. A longer feeding trial or use of different carbohydrate levels in combination with carbohydrate sources may yield more promising results.
Practical diet development for largemouth bass - lipid components
Rebecca Lochmann

Largemouth bass raised in Arkansas currently received trout diets that are high in fish meal and oil. These diets are costly to make and ship to Arkansas. It is likely that more economical and environmentally friendly ingredients such as plant and poultry products can be substituted in the diets of the bass without impairing their production.

A feeding trial was conducted in tanks under controlled conditions at UAPB. The fish were fed diets with different lipids including fish, poultry and plant sources for 10 weeks. A second trial was completed using diets with no fish meal and the same lipid sources from Trial 1.

In trial 1 growth and survival of the fish was the same on all diets regardless of lipid source. Alternative complement activity was higher in fish fed diets with n-3 fatty acids, either canola or menhaden fish oil. Fatty acid composition of the fillets reflected that of the diets. Results from Trial 2 are still being analyzed, but both growth and survival of LMB were compromised by total removal of fish meal from the diets. The substitution of poultry and plant oils in diets for largemouth bass to the extent possible without compromising production could decrease feed cost by as much as 20%.